I think it's best to go with an elimination routine principle here. The best would be to prepare the super simple green tea DIY toner Sarah introduced in the respective lesson. If this one causes the same effect it might be that the concentration of ingredients is too strong for her hair folicles. In that case it would be better to stop using this method. Washing your hairs after 4 days isn't too bad of a result at all and she might be ok to use a gentle shampoo on day 4 if she didn't opt for any silicones that need a sulfate to remove residue. Scalp toning isn't a must if you're already blessed with not having to wash your hair every other day.